code: def _tracker(self, seed, first_step, streamline):
      return local_tracker(
          self.direction_getter,
          self.stopping_criterion,
          seed,
          first_step,
          self._voxel_size,
          streamline,
          self.step_size,
          self.fixed_stepsize,
      )
  
file_path: dipy/dipy/tracking/local_tracking.py
imports: import random
  from collections.abc import Iterable
  from warnings import warn
  import numpy
  from dipy.tracking.localtrack import local_tracker, pft_tracker
  from dipy.tracking.stopping_criterion import AnatomicalStoppingCriterion, StreamlineStatus
  from dipy.tracking import utils
  from dipy.utils import fast_numpy
label_desc: Use image node_id 3 for calling the LocalTracking obj's underlying member method code with example usage: obj._tracker(seed, first_step, streamline) and returns: local_tracker